Technologies that optimise home solar are still too expensive

Roof-top solar can be a critical way to cut carbon emissions from electricity use, but unsubsidised payback periods are still too long, where one critical missing piece is a cheap device to ensure households use as much of their home generation as possible.

As battery prices fall further, these will become a critical part of home solar systems, by allowing home owners to store solar until they need it, including after sunset. But in the meantime, are there cheaper, alternative devices available?

I attended one of Europe’s bigger energy technology conferences last week, European Utility Week, and was surprised, first by how few “smart home” vendors could optimise home solar systems, and second, how expensive these were.

In a post-renewables subsidies world, households have to maximise self-consumption rates, meaning use as much home solar generation as possible for themselves, rather than export this to the grid.

In the days of subsidies, you could earn lucrative feed-in tariffs from exporting solar power to the grid. In a world beyond subsidies, where the export tariff is minimal or even zero, home solar only stacks up if you can displace expensive grid electricity by using this solar generation yourself.

You can maximise home solar by running appliances or heating water while the sun is shining. Many of us are away some or most of the time. Ideally, we need a smart device that automatically runs a scenario chosen by us, to eliminate exports to the grid. Such a scenario could charge a battery first, if there is one, and then, say, heat water via an immersion heater or electric heat pump, and once the maximum possible electricity is stored in the battery or as hot water, then run appliances such as washing machines.

At the Utility Week market fair last week, I found rather few vendors capable of such solar optimisation, as I randomly approached 13 vendors that identified themselves as smart home energy specialists.

Of these 13, nine couldn’t automate home solar. Instead, they offered data management, for example displaying home electricity use, offering tips on energy saving, and allowing remote operation of appliances and lights via a smart phone. Most required a smart meter already installed. Their systems cost from around €20 to €150. Some came free with other purchases, say of a ground-source heat pump. Several said that they were working on solar optimisation, as their “next step”.

Just four vendors stated that they could optimise solar use, by running scenarios to run appliances including batteries and water heaters, deliberately to minimise or eliminate grid exports. Two of these quoted prices of €500-€1,000. Given the additional capital cost to install a solar system in the first place, this would seem prohibitive for most people.

At the Utility Week trade fair, I was also really surprised by the payback period on solar systems, as estimated by Spanish solar installation data specialist, Ezzing Solar, which markets via suppliers such as Viesgo Solar in Spain and Wekiwi Solar in Italy. These long payback periods illustrate why it is so important to optimise home systems.

Ezzing Solar seems to have really smart software, which allows you to estimate the electricity generation and cost of a home solar system, in Spain or Italy, just by typing an address and selecting a roof. But the answers are a bit worrying, especially in Spain, presumably because of the cost of installation, including taxes, and not the quality of the sun, as Europe’s sunniest country!

A casual, uniformed use of the Wekiwi Solar simulations suggests an approximately five to six-year payback on the upfront cost of an installation on a south-facing roof in Italy – which appears attractive and could appeal to households. Get that below three years, and it really starts to make sense. But the Viesgo Solar simulations indicate a payback period of 18-20 years in Spain. This makes no sense, and should be a concern for policymakers in the new government there. It would be interesting to know what the impact will be of Spain’s recent decision to scrap the so-called solar tax, and cut the red tape associated with installing residential solar.